1. Field of the Invention
The present invention relates generally to the examination of pearls and, more particularly, to positively identifying natural pearls, and to measuring the thickness of the nacre coating of cultured pearls.
The jewelry industry's standard manual for identifications declares that the distinction between natural pearls and cultured pearls is the industry's most difficult distinction, even for gem experts, and for lack of any non-destructive alternative, requires X-ray examination by special laboratories. Such an examination may be inconvenient or impossible in many business situations.
Thus, there is widespread general confusion, even among experts, that has endured all of the approximately 100 years since advent of cultured pearls. Most jewelers are aware in a general way of the cultured pearls pretense but find it profitable. Few of today's American customers have any acquaintance with natural pearls. Most have never owned any. Chiefly from estates, there are still in private hands many natural pearls, singly or in necklaces, and these may confront the trader with decisions between a few hundred dollars and thousands.
The United States has imported in a year as much as 500 million dollars worth of cultured pearls and cultured pearl jewelry. Most such pearls are composed of more than 90 percent mother-of-pearl bead made from Mississippi or Tennessee river clamshell that costs about 30 cents per pound. The clamshell beads were found to be compatible material which when surgically inserted into the oyster, caused fewer mortalities of the host mollusks.
Many years ago, pearl culturers worked toward a one-half millimeter addition of nacre (calcium carbonate) as representing good quality cultured pearls. This might require as much as three years of nurture. Many cultured pearls subsequently have been created with only a few months of nurture and, consequently, have a nacre coating of negligible thickness. Often, the nacre coating is so thin that striations of the mother-of-pearl bead can be seen therethrough. Moreover, the reduced thickness of the nacre coating adversely affects the durability of the cultured pearl. The transition of the cultured pearl industry from a confined one of relatively few producers and subject to strict quality controls to one of many producers, some of which market cultured pearls that are too thinly coated with nacre, puts forth serious problems.
As in the distinction between natural pearls and cultured pearls, for lack of any non-destructive alternative, X-ray examination by special laboratories is required to determine the thickness of the nacre coating of cultured pearls. Again, such an examination may be inconvenient or impossible in many business situations.
2. Description of the Related Art
In the past, there have been many efforts and devices to distinguish between natural and cultured pearls. None were practical, convenient and certain.
One such distinguishing method required a hole to be drilled through the pearl. A tiny mirror and light were then inserted, and there might be seen the circular lines of nacre coating. Another method was to measure and compare the specific gravity of a pearl against the known number for natural pearl. It is sometimes suggested that a way to identify cultured pearls in a necklace is to hold the necklace in a straight line on white paper beneath a lamp, then rotate the pearls to observe whether they show a flash when the mother-of-pearl beads reach an aspect at which light is reflected. Flashing would be from the bright plane of individual mother-of-pearl beads and would occur twice in 360 degrees. Inasmuch as the mother-of-pearl beads are drilled at random, such coincidence is chancy. Moreover, this technique offers nothing to positively identify natural pearls. All these and other attempts fall short of anything for widespread use.
The most effective distinguishing method, and still the general last resort, has been X-ray examination. Likewise, X-ray examination can be used to determine the thickness of the nacre coating of a cultured pearl. However, X-ray examination is inconvenient, because it must be performed in special laboratories, which is an impossibility in many business situations.
A cultured pearl may be sawed or ground to expose the thickness of the nacre coating. However, this is a destructive examination procedure and merely measures the thickness of the nacre coating of the destroyed cultured pearl. Similarly, one may drill a hole through a cultured pearl, and examine the circular lines of the nacre coating with a tiny mirror and light inserted into the hole. Again, this is a destructive test and would merely provide a measure of the thickness of the nacre coating of the drilled-through cultured pearl.
Candling has been mentioned repeatedly relative to examining pearls. Candling, or backlighting to see the interior, has long been familiar for the detection of hens eggs with an embryo, to cull these from food marketing. Though candling may provide an identification of a cultured pearl, until the present invention, candling has not permitted accurate measurement of the thickness of the nacre coating of a cultured pearl.